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the AUTONOMIC reflex Arc: the effector neuron

begins in the CNS and ends in the periphery and is equivalent of the motorneuron


unlike the "withdrawal reflex" most of the integration of autonomic reflexes occurs

within the brain although at lower levels, brainstem, hypothalamus, rather than the cortex

afferents ALWAYS go to the brain


the ANS is part of peripheral nervous system that is specific for

smooth muscle and glands



fight or flight



rest and digest


ANS has ____ neurons in serious that will go to the effector cell

2 neurons


Neuron #1 in the ANS is the

preganglionic, starts in the CNS (gets message from brain), leaves the CNS, travels to ganglion where it synapses on the second neuron in the pathway


Neuron #2 in the ANS is

on the post ganglionic neuron, which then travels to the target organ and synapses on it


How can we distinguish between the parasympathetic and sympathetic systems?

1. where the preganglionic fibers leave the CNS
2. location of the ganglions
3. length of the pre-post ganglionic axons


Cranial and Sacral: which pre- ganglionic neurons leave from these two locations?

Thoracic and lumbar: which pre-ganglionic neurons leave from these two locations?

Parasympathetic C and S

Sym T and L


Where are the ganglia located in the parasympathetic nervous system?

Where are the ganglia located in the sympathetic?

Para: on or near the target organ
for the heart for instance, they are directly on the heart

Sym: from the sympathetic chain (mostly)


Sympathetic and Parasympathetic

short long or what

Para: PLS (parasym, long, then short)
Sym: SSL (sym, short, then long)


Pre and Post synapsing: what NT for para?
Post and effector synapsing: what NT for para?

1. acetylcholine, binds to nAChR on the post-ganglionic dendrite causing an EPSP and leading to an AP in the neuron

2. ACh as well


where are the nAChR on the post-ganglionic neuron in the parasympathetic nervous system?

on the dendrite, causing an influx of sodium
not voltage gated


Metaphor for PARA synapses 1 and 2

the first is like the mailman carefully placing mail through the mailbox, the second is like the mailman throwing the mail from his window as he's driving by (en pass, driving by)


what makes the second synapse (postgang syapsing on the effector) distinct?

1. the postgang releases ACh from vericosities into a less well defined juncture that isn't as protected, so substantial leakage of NT

2. the receptor on the effector is a mACh receptor (muscarinic receptor)


M receptors


M2: cardiac: ACh activates Gi subunit, DECREASES cAMP, increasing gK

M3: widely distributed in the body, Gq coupled

M3: autoreceptors on neurons, Gi coupled (decreases cAMP causing DECREASE in ACh release


ANS sympathetic: Pre-ganglionic NT



ANS sympathetic: Post-ganglionic R @ synapse 1

nAChR on the dendrite, but the nicotinic receptor is different than the one in the parasympathetic nervous system


ANS sympathetic: Post-gang synapsing on effector, NT

norepinephrine, which can bind to both alpha and beta adrenergic receptors


Adrenal Medulla

within medulla there are CHROMAFFIN cells that produce epinephrine (some dopamine and norepinephrine)
AM is equivalent of a sympathetic ganglion


What kind of neuron, neurotransmitter, and receptors are at work in the synapse with the adrenal medulla?

the synapse is between a preganglionic sympathetic neuron to release ACh to bind to an nAChR on the adrenal medulla chromaffin cells, causing it to release epinephrine to the blood

Preganglionic synapse acts on Chromaffin cells


Chromaffin cells primarily release epinephrine cells but they also release norepinephrine and some dopamine. Why is that?

dopamine --> norepinephrine --> epinephrine --> into the blood